Method for Detecting Coverage Loss in Broadband Wireless Access System

1. A method for performing a coverage loss detection procedure at a base station in a wireless communication system, the method comprising: transmitting an unsolicited advanced air interface ranging response (unsolicited AAI-RNG-RSP) message to a mobile station, wherein the unsolicited AAI-RNG-RSP message includes an indicator bit set to ‘1’ to request the mobile station to perform a ranging; starting a first timer when the unsolicited AAI-RNG-RSP message is transmitted; receiving an advanced air interface ranging confirmation (AAI-RNG-CFM) message including a station identifier (STID) of the mobile station after a successful periodic ranging, the AAI-RNG-CFM message indicating the successful periodic ranging initiated by the unsolicited AAI-RNG-RSP message; and starting a second timer if the AAI-RNG-CFM message is not received from the mobile station upon expiration of the first timer, wherein the second timer is related to a retention period of context of the mobile station.

2. The method according to claim 1 , further comprising: allocating uplink resources to the mobile station a predetermined number of times when a third timer expires, wherein the third timer starts upon completion of an initial network entry, wherein the unsolicited AAI-RNG-RSP message is transmitted when an arbitrary protocol data unit (PDU) is not received from the mobile station through the uplink resources during the predetermined number of times.

3. The method according to claim 1 , further comprising: releasing a dynamic context of the mobile station when the second timer expires.

4. The method according to claim 1 , wherein the first timer is a T58 timer and the second timer is a resource retain timer.

5. The method according to claim 1 , wherein the ranging is performed using a periodic ranging code.

6. A base station performing a coverage loss detection procedure in a wireless communication system, the base station comprising: a processor; and a radio frequency (RF) module for transceiving an RF signal controlled by the processor, wherein the processor is configured to: cause the RF module to transmit an unsolicited advanced air interface ranging response (unsolicited AAI-RNG-RSP) message to a mobile station, wherein the unsolicited AAI-RNG-RSP message includes an indicator bit set to ‘1’ to request the mobile station to perform a ranging; start a first timer when the unsolicited AAI-RNG-RSP message is transmitted; cause the RF module to receive an advanced air interface ranging confirmation (AAI-RNG-CFM) message including a station identifier (STID) of the mobile station after a successful periodic ranging, the AAI-RNG-CFM message indicating the successful periodic ranging initiated by the unsolicited AAI-RNG-RSP message; and start a second timer if the AAI-RNG-CFM message is not received from the mobile station upon expiration of the first timer, wherein the second timer is related to a retention period of context of the mobile station.

7. The base station according to claim 6 , wherein the processor is further configured to allocate uplink resources to the mobile station a predetermined number of times when a third timer expires, wherein the third timer starts upon completion of an initial network entry, wherein the unsolicited AAI-RNG-RSP message is transmitted when an arbitrary protocol data unit (PDU) is not received from the mobile station through the uplink resources during the predetermined number of times.

8. The base station according to claim 6 , wherein the processor is further configured to release a dynamic context of the mobile station when the second timer expires.

9. The base station according to claim 6 , wherein the first timer is a T58 timer and the second timer is a resource retain timer.

10. The base station according to claim 6 , wherein the ranging is performed using a periodic ranging code.